The production of various grades of ethylene polymer and copolymer telomer waxes in the presence of free radical initiators at elevated temperatures and pressures has been commercially practiced for some years, as described in U.S. Pat. Nos. 2,504,400, 2,683,141, and 2,712,534. The production of the hardest grades of such waxes, i.e., those having penetration hardness of less than about 3.0 (ASTM test D 1321-55T in 0.1 mm) however poses special problems and has been characterized by low production rates and high reactor fouling.
Various operating parameters affect the hardness of the resultant wax product; low temperature of polymerization are required to minimize the branching of polymer chains which decreases the crystallinity and softens the wax product. Low initiator and low telogen concentrations are required to produce the hardest grades of wax. These operating conditions have a deleterious effect on the production rate of these waxes. For example, the lower the initiator concentrations, the lower the production rate. Conversely, increasing the initiator concentrations will increase the production rate but produce a softer wax product. Increased initiator concentration also leads to increased reactor fouling. Fouling of the reactor, that is, deposition of polymer gels and high molecular weight polyethylene onto the walls of the reactor is a very serious problem in producing ethylene telomer waxes. Beside the obvious result of decreasing the volume of the reactor leading to decreased production rates and increasing "down time" of the reactor for cleaning, undue fouling also leads to decreased efficiency of reactor cooling. The consequent erratic changes in temperature which may result increase the dangers of a runaway reaction and explosion.
Another disadvantage to the formation of gels is that they have a deleterious effect on product emulsifiability by reducing emulsion clarity and producing grainy films. This demonstrates that optimum conditions for the production of hard waxes results in lowering the production rate.
In U.S. Pat. No. 3,888,911 there is described a continuous process for producing wax telomers of ethylene at high production rates and with minimal reactor fouling, which process comprises reacting ethylene and a telogen in the vapor phase at an elevated temperature and pressure in the presence of, as free radical initiator, at least one of t-butylperacetate, t-butylperoctoate, 1-cyano-1-(t-butylazo)cyclohexane, 2-(t-butylazo)isobutyronitrile and 2-t-butylazo-2-phenylpropane, the conversion (as therein defined) being maintained at from 55 to 75%.